In recent years, a modified semi-additive process (MSAP) has been widely employed for manufacturing printed circuit boards suitable for miniaturization of circuits. The MSAP is suitable for forming extremely fine circuits and is carried out using copper foil with a carrier to take its advantageous characteristics. For example, as shown in FIGS. 4 and 5, an extremely thin copper layer 118 of copper foil with a carrier is pressed against and tightly bonded to a resin substrate provided with a resin layer 122 on a core layer 124 having an inner conductor 126 using a primer layer 119, and then the carrier (not shown) is removed (step (a)). A via hole 128 is then formed by laser drilling, and the inside of the via hole 128 is desmeared (step (b)). After an electroless copper plating layer 130 is formed (step (c)), masking is performed in a predetermined pattern by exposure and development using a photoresist 131 (step (d)) and an electrolytic copper plating layer 132 is formed (step (e)). After the photoresist 131 is removed to form the wiring portion 132a (step (f)), unnecessary portions such as extremely thin copper foil between the adjacent wiring portions 132a are removed by flash etching over the entire thickness thereof (step (g)) to form a lead line 134 in a predetermined pattern.
In recent years, downsizing and sophistication of electronic devices, such as portable electronic devices, demand printed circuit boards having further miniaturized (fine-pitched) wiring patterns. To meet such a requirement, a copper foil for manufacturing a printed circuit board is desired to have a smaller thickness than current ones. Accordingly, a technique has been proposed for forming a copper foil layer for a copper foil with a carrier by vapor deposition such as sputtering. For example, Patent Document 1 (JP4726855B2) discloses a copper foil with a carrier sheet. The copper foil with a carrier sheet has a copper foil layer on the surface of the carrier sheet via a joint interface layer therebetween. The joint interface layer consists of two layers (a metal layer and a carbon layer) and the copper foil layer was prepared by forming a first copper layer having a thickness of 10 nm to 300 nm on the joint interface layer by physical vapor deposition and further forming a second copper layer by electrolysis. This document also discloses that the metal layer of the joint interface layer may be composed of any one of tantalum, niobium, zirconium, nickel, chromium, titanium, iron, silicon, molybdenum, vanadium, and tungsten. The copper foil with a carrier disclosed in Patent Document 1 has an industrially adoptable stable release strength between the carrier foil layer and the copper foil layer even at a pressing temperature exceeding 300° C.
A copper foil with a resin film carrier is known. For example, Patent Document 2 (JP2015-157472) discloses a copper foil with a release film. The copper foil with a release film consists of a copper layer provided on a release layer of a release film, and the release layer consists of a metal layer and a carbon layer formed in this order on the release film. According to this document, preferred examples of the metal layer include aluminum, zinc, titanium, chromium, iron, cobalt, nickel, germanium, platinum, gold, and lead, while preferred examples of the polymer of the film include polyimides, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, syndiotactic polystyrene films, aromatic polyamide films, modified polyphenylene ether films, fluorine-based films, and liquid crystal polymer films.